A coated type magnetic recording medium which is prepared by dispersing magnetic particles or ferromagnetic metal particles such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, Bertholide compound of .gamma.-Fe.sub.3 O.sub.4, and C.sub.r O.sub.2 in an organic binder such as a vinyl chloride-vinyl acetate copolymer, a styrene-butadiene copolymer, an epoxy resin or a polyurethane resin, coating the magnetic coating composition on a non-magnetic support and drying it has been widely used. With the recent demand for high density recording, various research and studies have been developed to manufacture a thin metal film type magnetic recording medium comprising as a magnetic recording layer a ferromagnetic thin metal film which is prepared by a vapor deposition method such as vacuum evaporation, sputtering, ion plating or plating such as electroplating or electroless plating without using a binder.
To realize high density recording of a magnetic recording medium, it has been theoretically and experimentally proposed to have a higher coercive force and to make the medium thinner. Therefore, a thin metal film type magnetic recording medium which can be made thinner by 1/10 time and can have a higher saturated magnetic flux density than a coated type magnetic recording medium has been greatly desired.
Particularly a vapor deposition method is very effective, because treatment of waste solution as is required for a plating method is unnecessary, the manufacturing process is simple and the rate for precipitating a film can be made higher. It is known that a magnetic film having a desirable coercive force and a squareness ratio in a magnetic recording medium can be prepared by an oblique vapor deposition method as one of the vacuum evaporation methods, as disclosed in U.S. Pat. Nos. 3,342,632 and 3,342,633. Further, a magnetic recording medium comprising a ferromagnetic metal thin film has problems such as weather resistance, running properties and wear resistance. Upon recording, reproducing and erasing magnetic signals, a magnetic recording medium is put in a high speed motion relative to the magnetic head. In this case, a magnetic recording medium should run smoothly and stably without making contact with the head causing wear and damage. In view of the above-described background, studies have been made to provide a lubricating layer and a protective layer in order to improve running properties and durability.
A protective layer used for a thin metal film type magnetic recording medium can be prepared by dissolving in organic solvents a thermoplastic resin, a thermosetting resin, a fatty acid, metal salts of a fatty acid, fatty acid ester or alkyl phosphate and the like and coating it, as disclosed, for example, in Japanese Patent Application (OPI) Nos. 69824/1985 and 85427/1985 (the term "OPI" as used herein means an "unexamined published application".)
However, there are still problems such as running properties and wear resistance of the resulting thin metal film type magnetic recording medium are not satisfactory and spacing loss between the head and the tape due to the thickness of the protective layer or the lubricating layer deteriorates electromagnetic properties. Therefore, improvements are still required for realizing a thin metal film type magnetic recording medium.